1. Field of the Invention
This invention relates to the field of the coloring of continuous synthetic filaments in the form of tow for conversion into yarn having the color known as "heather".
2. Description of the Prior Art
As used herein, the term "heather" which is a well known term of art, will refer to a product in the form of a yarn ultimately formed from staple and which has a color which is formed from the blending of white and colored pieces of staple or staple having white and colored portions thereon. Such heather yarns are conventionally used in the formation of fabrics for wearing apparel and the like, although, of course, many type of end uses are possible. While the term "heather" generally refers to the color, it has also become conventional to designate the product as heather.
There are currently two commercial methods for the production of heather. In the first method, a continuous synthetic fiber, such as, acrylic or polyester, although other synthetics may be used, which fiber is in the form of tow, is cut into staple and preformed into sliver. It is understood that the terms "staple" and "sliver" are well known and in particular, "sliver" refers to a rope formed from staple which has been blended sufficiently to give the rope some cohesiveness so that it may be further treated.
The sliver thus formed is then wound onto a bobbin which generally weighs from about 8 to 10 kg, although more or less weight can be used per bobbin depending on the particular type process which is going to be used as well as the type of synthetic fiber and its own weight. In any event, such bobbins are conventionally referred to as "tops".
A number of such tops are then placed onto a creel which may accommodate 16 or more of the tops. The sliver from each of the tops are then simultaneously (all the ends) fed through a gill box to form an extremely thin sheet which is referred to as a "lap". The lap is sufficiently thin so as to substantially expose most of the fibers to the subsequent processing.
This lap is then printed on one side by passing the lap between a print roll having a plurality of raised portions, generally in the form of a spiral thereon, and a second roll which is coated with an absorbent material and which is impregnated with dye. As a result, that side of the lap which contacts the impregnated roll is printed with a design pattern corresponding to that of the print roll. Moreover, because the print roll is in pressurized contact with the absorbent covering of the impregnated roll, the design pattern essentially impregnates through the thickness of the lap.
The design generally printed onto the lap results in the individual filaments of the sliver which, as noted, are formed from blended pieces of staple, having colored and uncolored portions. That is to say, the uncolored portions are the color of the original fiber which is essentially white.
The thus printed lap is then gathered, typically through a funnel type gathering device, and collected into essentially a single rope and treated using the usual dye fixation procedures, washing treatments, drying treatments, etc., such treatments being conventional and depending on both the type of dye and type of synthetic fiber that is being used.
After the fixation and subsequent processing treatments, the rope must then be reformed into sliver. The sliver is then formed into tops again for shipment to the processing center for the conventional blending treatments to prepare the yarn.
One of the significant disadvantages of the above process which is commonly referred to as the "Vigereux" process, is the fact that it can only be used to treat sliver, i.e., material which has been precut into staple. Thus, the process is completely unsuitable and cannot be used with tow, which is a rope formed from the fibers which are in continuous filament form
The basic reason for this is that tow cannot be treated by passing through a gill box because it is formed from continuous filament rather than from staple. Consequently, tow cannot be formed into a thin lap as can sliver. Also, tow as it comes from the manufacturer, has a crimp in it which results from the manufacturing process. Thus it has been thought that because of the inability to form tow into a lap, one cannot achieve the substantial impregnation of all of the fibers as is required in the Vigereux process to produce a suitable product for forming into heather.
The second method for forming heather is by cutting two, formed from continuous filaments, into staple, converting the staple into sliver, and then forming the sliver into tops. The tops are then subjected to a "package or unit type" dyeing operation wherein the individual tops are placed into sealable containers and are dyed in much the same way as in the conventional "package dyeing" procedure. This results, of course in the tops being 100 percent dyed with the particular color being used.
The thus dyed tops are fixed, washed, dried, etc., using conventional procedures and these dyed tops are then creeled with an appropriate number of undyed white tops, depending on the ultimate color blend which is desired in the heather. The ends of all of these creeled tops are then subjected to blending through a series of gills, blenders, etc., for preparation into a yarn.
The disadvantages of this process are apparent since the ultimate blending is obtained by taking sliver of one color and/or sliver of another color and uncolored sliver and blending these individual pieces. The pieces of sliver are relatively large and consequently, the homogeneity of the resulting heather is not particularly good due to the large splotches of color which will occur.
Turning again to the Vigereux process, a number of other disadvantages attend the utilization of this process. For example, it is relatively slow because of the necessity of using the gill box. The gill box essentially separates the fibers of the sliver in such a way that a suitably thin lap can be formed. This is, however, an extremely slow process and consequently, the speed of the subsequent printing step is controlled by the speed of the gill box treatment.
Another problem is the fact that, in the Vigereux process, extensive breaks in the form of "wrap-arounds" on the print wheel occur. This is primarily due to the fact that the lap is extremely thin and is composed of cut fibers. Thus, many fiber ends pass through the print roll and covered roll and the chances for the ends catching on to the roll and wrapping around the roll are very high.
Moreover, since, in the Vigereux type process, one is feeding a series of 16 or more different ends of sliver into the machine, and this sliver is composed of cut fibers, from time to time, due to a slight catch in the tops, the sliver will pull apart or break. This, like the "wrap-arounds" necessitates shutting down of the machine in order to tie the slivers or remove the wrap-arounds.
In practice, two workers are required to monitor the Vigereux process at all times. One of the workers monitors the print roll to continually remove any small wrap-arounds which are formed so as to avoid their expanding into large wrap-around. The other worker is required to continuously monitor the creel so as to repair any breaks in the sliver.
With respect to the second process described hereinabove, one of the major disadvantages is that it is essentially a bulk type dyeing process. That is to say, the tops are placed within a chamber and dye stuff in a relatively large volume of solvent is forced through the tops under pressure. In dyeing processes of this type, the efficiency of the dye usage is relatively poor. After the dyeing operation, not all of the dye is exhausted from the dyeing liquid. However, this dyeing liquid is no longer usable and is generally discarded. Consequently, the process is quite expensive considering the amount of dye wasted in the process, the large amount of energy required and the large amount of solvent or water wasted.
Another problem of this process is the fact that it creates pollution problems. Thus, the used dyestuff solution must be discarded and, assuming that the solvent is water, it will generally be disposed of in conventional sewage. However treatment may be required to properly prepare it for entry into the sewage system.
In the event that an organic solvent system is used, the solvent cannot be dumped but rather, must be recovered. Also, of course, such organic solvents create air pollution problems and cannot be vented to the atmosphere. Also, organic solvents, are relatively expensive and, consequently, processes are usually required in the overall treatment to recover as much of the solvent as possible. This, of course, adds to the overall expense of the process.
Finally, because dyestuffs diluted in large volumes of solvent, are utilized in this type process, relatively large volumes are constantly being treated and this is another disadvantage of the process, since larger equipment is needed.
Also, in this unit dyeing type of process, when it is desired to change colors, the down-time is quite extensive since all of the equipment must be completely cleaned and all contamination of the old dyestuff must be removed from the dye tanks. This is a fairly intricate process and requires a significant amount of time in practice.
One important aspect of the so-called "package-dyeing" system is that when a mixture of dyestuffs is to be used to achieve a given color, the dyes must be compatible with respect to their exhaust rates from the dye bath. That is to say, their exhaust rate curves must be similar. If they are not compatible and do not have the same or similar exhaustion rates, uneven dyeing will occur.
Consequently, the choice of dyestuffs for use in such combinations is quite limited with this process and often result in the necessity of utilizing relatively expensive dyes in order to obtain the appropriate compatibility.
A major problem attendant both to the Vigereux type process as well as the unit or package dyeing type process described above is the fact that they both treat sliver which is formed from staple and cannot be utilized to treat tow. This has a significant effect on acrylic fiber when it is desired to have a "high bulk yarn". In producing such a high bulk, the bulk is usually imparted to the acrylic fiber at the time of cutting it into staple. Thus, the bulk is imparted to the undyed fiber.
However, in both the Vigereux and the unit dyeing process, the staple is ultimately dyed and thus must necessarily be subjected to dye fixation treatments. Such treatments usually involve heating of the sliver. As a result of this second heating the original high bulk which was imparted to the fiber is destroyed. Consequently, a heather product having high bulk cannot be produced by either the Vigereux or the unit dyeing process because of the necessity of the subsequent dye fixation treatments which destroy the high bulk previously imparted to the fiber.
It is also possible, with acrylic fibers, to produce heather utilizing the so-called "tunnel dyeing" technique. This enables acrylic fiber to be dyed in the form of tow. However, the fiber passed through the "tunnel dyeing" process, which is a conventional process, is completely dyed with the particular color.
However, the tunnel dyeing technique has a number of disadvantages, one of which is the fact that because of the speed of the process and the narrowness of the dyeing chamber where the dye is aged and steamed after being applied to the fiber, the dyes often do not set exactly properly. Thus, for example, if one is using a dye composition composed of several colors, the tow exiting the chamber will often be observed to have spots of the individual colors thereon rather than a blend of the colors. This is due to the fact that the exact steaming or other finishing treatment conditions were not sufficient for each of the individual colors. While it is possible to subsequently blend the thus dyed material in such a manner as to obliviate the inhomogeneity resulting from the dyeing, when another batch of tow is treated in an attempt to obtain the same color, it cannot be done since it is virtually impossible to duplicate the non-homogeneity that occurred in the previous batch.
Also, of course, with respect to the tunnel dyeing technique, in order to form the heater product, an ultimate blending of individual slivers must be effected as with the unit dyeing treatment.